An aircraft passenger seat with an adjustable seat depth is disclosed in U.S. Pat. No. 5,560,681. The changing of the seat depth within certain limits in the case of such seats significantly contributes to the comfort of the seat occupant. The distance between seat front edge and backrest may be adjusted to the distance between the hollow of the knee and the buttocks of a particular seat occupant. This adjustment is an advantage in the case of seats for commercial aircraft, in which an effort must be made to achieve maximum seat comfort in view of the extended duration of the flights involved. Adjustment of the seat depth is also favorable in the case of such seats if a folding or pivoting leg rest adjoins the seat front edge.
Adjustment of the seat depth is also important for modern aircraft passenger seats, as are used in the business class and first class compartments (see, e.g., DE 102 20 248 C1). Such seat can form a bed position in which the back-tilted backrest is designed to form an essentially integrated reclining surface together with the seat component and the leg rest, even for taller individuals. The additional reclining surface achieved with the extended leg rest still would not be enough to create in the aggregate a long total reclining surface. As a result of the additional displacement of the seat front edge forward, the leg rest is moved forward as a result of coupling of this leg rest with the seat frame or seat cushion carrier. If the support surface in this reclined position is lacking, an extension movement of 3 to 6 centimeters may be enough to create a pleasant comfort or bed position, even for very tall individuals. An additional advantage is achieved in that any gap between the upper end of the leg rest and the seat cushion carrier is closed.
U.S. Pat. No. 5,560,681 discloses an actuating or adjustment mechanism including a set of levers mounted between seat frame and seat cushion carrier, and pretensioning a pressure spring for movement displacing the seat cushion carrier to increase the seat depth so as to make a clear-cut seat depth adjustment possible. In the disclosed solution, the pressure spring normally is blocked by a hydraulic cylinder, which cylinder may be unblocked by hydraulic means, so that the force of the released spring displaces the seat cushion carrier forward. To move the seat cushion carrier again to reduce the seat depth, the seat occupant must unblock the hydraulic cylinder and move the seat cushion carrier back manually against the force of the pressure spring.
Aside from the exertion of effort by the seat occupant and a corresponding expenditure of force required of the seat occupant to reduce the seat depth, the structural configuration of the actuating mechanism in the form of a set of levers with a pressure spring and a hydraulic cylinder provided for blocking in seats of this type is relatively large. The structural space required for the structural component and associated link joints is a disadvantage. In particular, the large number of components results in a high weight for the respective aircraft passenger seat, something which is undesirable for obvious reasons (e.g., fuel costs). In addition, continuously reliable operation is not always guaranteed, because of the complexity of the lever mechanism.